How are infrared and ultraviolet radiations, which are invisible to the eye, detected? Detailed answer

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How are infrared and ultraviolet radiations, which are invisible to the eye, detected? Detailed answer

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How are infrared and ultraviolet radiations, which are invisible to the eye, detected?

In 1800, the English astronomer and optician William Herschel (1738-1822) performed a very simple but interesting experiment, intending to test whether heat, as was then commonly believed, was indeed evenly distributed over the solar spectrum.

Moving the thermometer along the solar spectrum, Herschel discovered that the temperature indicated by it not only increased continuously when moving from the ultraviolet end of the spectrum to the red, but its maximum was generally reached in the region lying beyond the red part of the spectrum, that is, where the eye does not see any light. . Herschel explained this phenomenon by invisible thermal radiation emanating from the Sun and deflected by a prism weaker than red, which is why it was called infrared (below red).

In 1801, the German physicist Johann Wilhelm Ritter (1776-1810) made another discovery "symmetrical" to Herschel's and equally important. He set out to investigate the chemical action of various parts of the light spectrum. To do this, he used silver chloride, the blackening of which under the action of rays was discovered back in 1727 by Johann Heinrich Schulze (1687-1744).

Ritter found that the chemical effect of radiation increases gradually along the spectrum from the red end to the violet and reaches a maximum beyond the violet region - where the eye no longer perceives any light. Thus, a new radiation was found in the spectrum, which is present in sunlight and is refracted by a prism stronger than violet, in connection with which it was called ultraviolet (higher than violet).

Almost simultaneously with Ritter, ultraviolet radiation was discovered by the English scientist William Hyde Wollaston (1766-1828), who conducted similar experiments with a solution of gummigut, which changes its color from yellow to green under the action of light.

Author: Kondrashov A.P.

Random interesting fact from the Great Encyclopedia:

What is a calorie?

Today, it seems, almost everyone is "monitoring their calories." There are even restaurants that print the number of calories in each dish right on the menu. To understand what a calorie is and what role it plays in the body, let's start with a food item in general.

Today, science still cannot explain exactly how the cell converts food into energy. We just know that it is. And we also cannot explain why this cell of the body needs certain and not some other products for its normal functioning.

We know that when food enters the body, it combines with oxygen. We can say that it "burns" like fuel. The work that fuel does is what we measure today in terms of calories.

A gram-calorie, or small calorie, is the amount of heat required to raise the temperature of one gram of water by one degree Celsius. A large calorie is equal to 1000 small ones. When measuring the energy value of food, we usually use a large calorie.

Each type of food, "burning down", supplies a certain amount of calories. For example, one gram of protein provides four calories, one gram of fat - nine. The body doesn't care what fuel is used to produce energy, as long as that energy is sufficient to sustain life.

The number of calories a person needs depends on the work he does. For example, a person weighing approximately 68 kilograms needs only 1680 calories per day if he is in a state of absolute rest. If he does moderate work, such as office work, that figure jumps to 3360 calories a day. And if a person is engaged in hard work, it will take 6720 calories per day for the body to function normally.

Children need more calories than adults because older people cannot burn fuel as quickly. Surprisingly, we burn more calories in winter than in summer. The usual fuel for humans is carbohydrates, starch and sugar. And what, you ask, if we absorb more fuel than we need? The body will use up as much as it needs and set aside some for future use. He can put off about one-third of his daily allowance. The rest turns into fat! That's why we diet.

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Researchers from the Virginia Tech School of Medicine (USA) have introduced a new method of combating physical pain based on the use of ultrasound.

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The effectiveness of the method was demonstrated on 23 healthy volunteers suffering from pain: the pain, although not completely, was significantly reduced.

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